Radiofrequency coils have been developed that can be used as intravenous or arterial or alimentary catheters. These catheters were placed in the right and left ventricle and at various locations along the alimentary canal of anesthetized dogs under fluoroscopic observation. 31P and 1H NMR signals were then obtained from these coils. 31P NMR signals were detected from creatine phosphate, inorganic phosphate and adenosine triphosphate with adequate signal to noise within five minutes. This technique will be extremely useful in investigating the in vivo energy metabolism of internal organs with minimal surgical intervention.